Changes in Aerobic Plate and Escherichia coli–Coliform Counts and in Populations of Inoculated Foodborne Pathogens on Inshell Walnuts during Storage

2016 ◽  
Vol 79 (7) ◽  
pp. 1143-1153 ◽  
Author(s):  
JOHN C. FRELKA ◽  
GORDON R. DAVIDSON ◽  
LINDA J. HARRIS
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Relative Humidity ◽  
Low Temperature ◽  
Foodborne Pathogens ◽  
Limit Of Detection ◽  
Sampling Time ◽  
E Coli ◽  
Plate Counts ◽  
Forced Air

ABSTRACT After harvest, inshell walnuts are dried using low-temperature forced air and are then stored in bins or silos for up to 1 year. To better understand the survival of bacteria on inshell walnuts, aerobic plate counts (APCs) and Escherichia coli–coliform counts (ECCs) were evaluated during commercial storage (10 to 12°C and 63 to 65% relative humidity) over 9 months. APCs decreased by 1.4 to 2.0 log CFU per nut during the first 5 months of storage, and ECCs decreased by 1.3 to 2.2 log CFU per nut in the first month of storage. Through the remaining 4 to 8 months of storage, APCs and ECCs remained unchanged (P > 0.05) or decreased by <0.15 log CFU per nut per month. Similar trends were observed on kernels extracted from the inshell walnuts. APCs and ECCs were consistently and often significantly higher on kernels extracted from visibly broken inshell walnuts than on kernels extracted from visibly intact inshell walnuts. Parameters measured in this study were used to determine the survival of five-strain cocktails of E. coli O157:H7, Listeria monocytogenes, and Salmonella inoculated onto freshly hulled inshell walnuts (~8 log CFU/g) after simulated commercial drying (10 to 12 h; 40°C) and simulated commercial storage (12 months at 10°C and 65% relative humidity). Populations declined by 2.86, 5.01, and 4.40 log CFU per nut for E. coli O157:H7, L. monocytogenes, and Salmonella, respectively, after drying and during the first 8 days of storage. Salmonella populations changed at a rate of −0.33 log CFU per nut per month between days 8 and 360, to final levels of 2.83 ± 0.79 log CFU per nut. E. coli and L. monocytogenes populations changed by −0.17 log CFU per nut per month and −0.26 log CFU per nut per month between days 8 and 360, respectively. For some samples, E. coli or L. monocytogenes populations were below the limit of detection by plating (0.60 log CFU per nut) by day 183 or 148, respectively; at least one of the six samples was positive at each subsequent sampling time by either plating or by enrichment.

scholarly journals Growth of Salmonella and Other Foodborne Pathogens on Inoculated Inshell Pistachios during Simulated Delays between Hulling and Drying

2019 ◽  
Vol 82 (5) ◽  
pp. 815-825 ◽  
Author(s):  
MAHTA MOUSSAVI ◽  
VANESSA LIEBERMAN ◽  
CHRIS THEOFEL ◽  
JAVAD BAROUEI ◽  
LINDA J. HARRIS
Keyword(s):  
Escherichia Coli ◽  
Relative Humidity ◽  
Foodborne Pathogens ◽  
Lag Time ◽  
Escherichia Coli O157 ◽  
Contributing Factors ◽  
Shell Surface ◽  
E Coli ◽  
Significant Growth ◽  
Lower Maximum

ABSTRACT During harvest, pistachios are hulled, separated in water into floater and sinker streams (in large part on the basis of nut density), and then dried before storage. Higher prevalence and levels of Salmonella were previously observed in floater pistachios, but contributing factors are unclear. To examine the behavior of pathogens on hulled pistachios during simulated drying delays, floater and sinker pistachios collected from commercial processors were inoculated at 1 or 3 log CFU/g with cocktails of Salmonella and in some cases Escherichia coli O157:H7 or Listeria monocytogenes and incubated for up to 30 h at 37°C and 90% relative humidity. Populations were measured by plating onto tryptic soy agar and appropriate selective agars. In most cases, no significant growth (P > 0.05) of Salmonella was observed in the first 3 h after inoculation in hulled floaters and sinkers. Growth of Salmonella was greater on floater pistachios than on corresponding sinkers and on floater pistachios with ≥25% hull adhering to the shell surface than on corresponding floaters with <25% adhering hull. Maximum Salmonella populations (2 to 7 log CFU/g) were ∼2-log higher on floaters than on corresponding sinkers. The growth of E. coli O157:H7 and Salmonella on hulled pistachios was similar, but a longer lag time (approximately 11 h) and significantly lower maximum populations (4 versus 5 to 6 log CFU/g; P < 0.05) were predicted for L. monocytogenes. Significant growth of pathogens on hulled pistachios is possible when delays between hulling and drying are longer than 3 h, and pathogen growth is enhanced in the presence of adhering hull material.

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on Plastic Kitchen Cutting Boards by Electrolyzed Oxidizing Water

1999 ◽  
Vol 62 (8) ◽  
pp. 857-860 ◽  
Author(s):  
KUMAR S. VENKITANARAYANAN ◽  
GABRIEL O. I. EZEIKE ◽  
YEN-CON HUNG ◽  
MICHAEL P. DOYLE
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Laminar Flow ◽  
Foodborne Pathogens ◽  
Deionized Water ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Laminar Flow Hood ◽  
Cutting Boards ◽  
Temperature Time

One milliliter of culture containing a five-strain mixture of Escherichia coli O157:H7 (∼1010 CFU) was inoculated on a 100-cm2 area marked on unscarred cutting boards. Following inoculation, the boards were air-dried under a laminar flow hood for 1 h, immersed in 2 liters of electrolyzed oxidizing water or sterile deionized water at 23°C or 35°C for 10 or 20 min; 45°C for 5 or 10 min; or 55°C for 5 min. After each temperature–time combination, the surviving population of the pathogen on cutting boards and in soaking water was determined. Soaking of inoculated cutting boards in electrolyzed oxidizing water reduced E. coli O157:H7 populations by ≥5.0 log CFU/100 cm2 on cutting boards. However, immersion of cutting boards in deionized water decreased the pathogen count only by 1.0 to 1.5 log CFU/100 cm2. Treatment of cutting boards inoculated with Listeria monocytogenes in electrolyzed oxidizing water at selected temperature–time combinations (23°C for 20 min, 35°C for 10 min, and 45°C for 10 min) substantially reduced the populations of L. monocytogenes in comparison to the counts recovered from the boards immersed in deionized water. E. coli O157:H7 and L. monocytogenes were not detected in electrolyzed oxidizing water after soaking treatment, whereas the pathogens survived in the deionized water used for soaking the cutting boards. This study revealed that immersion of kitchen cutting boards in electrolyzed oxidizing water could be used as an effective method for inactivating foodborne pathogens on smooth, plastic cutting boards.

scholarly journals Efficacy of Electrolyzed Oxidizing Water for Inactivating Escherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes

1999 ◽  
Vol 65 (9) ◽  
pp. 4276-4279 ◽  
Author(s):  
Kumar S. Venkitanarayanan ◽  
Gabriel O. Ezeike ◽  
Yen-Con Hung ◽  
Michael P. Doyle
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Salmonella Enteritidis ◽  
Sampling Time ◽  
Deionized Water ◽  
Escherichia Coli O157 ◽  
Water Control ◽  
E Coli ◽  
Complete Inactivation ◽  
Control Samples

ABSTRACT The efficacy of electrolyzed oxidizing water for inactivatingEscherichia coli O157:H7, Salmonella enteritidis, and Listeria monocytogenes was evaluated. A five-strain mixture of E. coli O157:H7,S. enteritidis, or L. monocytogenes of approximately 108 CFU/ml was inoculated in 9 ml of electrolyzed oxidizing water (treatment) or 9 ml of sterile, deionized water (control) and incubated at 4 or 23°C for 0, 5, 10, and 15 min; at 35°C for 0, 2, 4, and 6 min; or at 45°C for 0, 1, 3, and 5 min. The surviving population of each pathogen at each sampling time was determined on tryptic soy agar. At 4 or 23°C, an exposure time of 5 min reduced the populations of all three pathogens in the treatment samples by approximately 7 log CFU/ml, with complete inactivation by 10 min of exposure. A reduction of ≥7 log CFU/ml in the levels of the three pathogens occurred in the treatment samples incubated for 1 min at 45°C or for 2 min at 35°C. The bacterial counts of all three pathogens in control samples remained the same throughout the incubation at all four temperatures. Results indicate that electrolyzed oxidizing water may be a useful disinfectant, but appropriate applications need to be validated.

Fate of Listeria monocytogenes, Salmonella Typhimurium DT104, and Escherichia coli O157:H7 in Labneh as a Pre- and Postfermentation Contaminant

2000 ◽  
Vol 63 (5) ◽  
pp. 608-612 ◽  
Author(s):  
MOHSEN S. ISSA ◽  
ELLIOT T. RYSER
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Salmonella Typhimurium ◽  
Foodborne Pathogens ◽  
Storage Temperature ◽  
Starter Culture ◽  
Salt Content ◽  
Health Concern ◽  
Escherichia Coli O157 ◽  
E Coli

Commercially pasteurized milk (∼2% milkfat) was heated at 85 to 87°C/30 min, inoculated to contain 2,000 to 6,000 CFU/ml of Listeria monocytogenes, Salmonella Typhimurium DT104, or Escherichia coli O157:H7, cultured at 43°C for 4 h with a 2.0% (wt/wt) commercial yogurt starter culture, stored 12 to 14 h at 6°C, and centrifuged to obtain a Labneh-like product. Alternatively, traditional salted and unsalted Labneh was prepared using a 3.0% (wt/wt) starter culture inoculum, similarly inoculated after manufacture with the aforementioned pathogens, and stored at 6°C and 20°C. Throughout fermentation, Listeria populations remained unchanged, whereas numbers of Salmonella increased 0.33 to 0.47 logs during the first 2 h of fermentation and decreased thereafter. E. coli populations increased 0.46 to 1.19 logs during fermentation and remained that these levels during overnight cold storage. When unsalted and salted Labneh were inoculated after manufacture, Salmonella populations decreased >2 logs in all samples after 2 days, regardless of storage temperature, with the pathogen no longer detected in 4-day-old samples. Numbers of L. monocytogenes decreased from 2.48 to 3.70 to <1.00 to 1.95 logs after 2 days with the pathogen persisting up to 15 days in one lot of salted/unsalted Labneh stored at 6°C. E. coli O157:H7 populations decreased from 3.39 to 3.7 to <1.00 to 2.08 logs during the first 2 days, with the pathogen no longer detected in any 4-dayold samples. Inactivation rates for all three pathogens in Labneh were unrelated to storage temperature or salt content. Unlike L. monocytogenes that persisted up to 15 days in Labneh, rapid inactivation of Salmonella Typhimurium DT104 and E. coli O157:H7 suggests that these emerging foodborne pathogens are of less public health concern in traditional Labneh.

Inhibition and Inactivation of Five Species of Foodborne Pathogens by Chitosan

1992 ◽  
Vol 55 (11) ◽  
pp. 916-919 ◽  
Author(s):  
GUANG-HUA WANG
Keyword(s):  
Escherichia Coli ◽  
Staphylococcus Aureus ◽  
Antibacterial Activity ◽  
Acetic Acid ◽  
Listeria Monocytogenes ◽  
Salmonella Typhimurium ◽  
Yersinia Enterocolitica ◽  
Foodborne Pathogens ◽  
E Coli ◽  
No Inhibition

Inhibition and inactivation of five species of foodborne pathogens (Staphylococcus aureus, Escherichia coli, Yersinia enterocolitica, Listeria monocytogenes, and Salmonella typhimurium) by chitosan were studied. Nutrient broths were supplemented with 0, 0.5, 1.0, 1.5, 2.0, and 2.5% chitosan, adjusted to pH 6.5 or 5.5 with 2% acetic acid, and incubated at 30°C. The outgrowths of these bacteria were observed. At pH 6.5, in general, antibacterial activity of chitosan was relatively weak. The effectiveness of chitosan against S. aureus was greatest, followed by S. typhimurium, E. coli, and Y. enterocolitica. As the concentration of chitosan increased, the effectiveness of chitosan against these four species of pathogens also increased. No inhibition of L. monocytogenes by chitosan occurred. At pH 5.5, presence of chitosan inactivated these pathogens except that 0.5% chitosan did not affect the growth of S. typhimurium. Thus, the antibacterial activity of chitosan was stronger at pH 5.5 than at pH 6.5.

Antimicrobial Efficacy of Eugenol Microemulsions in Milk against Listeria monocytogenes and Escherichia coli O157:H7

2007 ◽  
Vol 70 (11) ◽  
pp. 2631-2637 ◽  
Author(s):  
SYLVIA GAYSINSKY ◽  
T. MATTHEW TAYLOR ◽  
P. MICHAEL DAVIDSON ◽  
BARRY D. BRUCE ◽  
JOCHEN WEISS
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Foodborne Pathogens ◽  
Milk Fat ◽  
Skim Milk ◽  
Surfactant Solution ◽  
Lag Phase ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Resistant Strains

The antimicrobial activity of eugenol microemulsions (eugenol encapsulated in surfactant micelles) in ultrahigh-temperature pasteurized milk containing different percentages of milk fat (0, 2, and 4%) was investigated. Antimicrobial micro-emulsions were prepared from a 5% (wt) aqueous surfactant solution (Surfynol 485W) with 0.5% (wt) eugenol. Two strains each of Listeria monocytogenes and Escherichia coli O157:H7 previously shown to be the least and most resistant to the microemulsion in microbiological media were used to inoculate sterile milk (104 CFU/ml). Samples were withdrawn and plated at 0, 1, 3, 6, 12, and 24 h for enumeration. Microemulsions completely prevented growth of L. monocytogenes for up to 48 h in skim milk and reduced both strains of E. coli O157:H7 to less than detectable levels in less than 1 h. Similarly, in 2% fat milk, eugenol-Surfynol combinations reduced both strains of E. coli O157:H7 to less than detectable levels in less than 1 h but only increased the lag phase of both strains of L. monocytogenes. In full-fat milk (4% fat), microemulsions inhibited growth of the least resistant strains of L. monocytogenes and E. coli but were ineffective against the two resistant strains. Unencapsulated eugenol was slightly more or as inhibitory as microemulsions against target pathogens. Results were attributed to diffusional mass transport of antimicrobials from microemulsions to the macroemulsion (milk). Results suggest that food composition, especially fat level, may affect the efficiency of targeting of foodborne pathogens with surfactant-encapsulated antimicrobials.

Survival and Recovery of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on Lettuce and Parsley as Affected by Method of Inoculation, Time between Inoculation and Analysis, and Treatment with Chlorinated Water

2004 ◽  
Vol 67 (6) ◽  
pp. 1092-1103 ◽  
Author(s):  
MEGAN M. LANG ◽  
LINDA J. HARRIS ◽  
LARRY R. BEUCHAT
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Foodborne Pathogens ◽  
Escherichia Coli O157 ◽  
Water Control ◽  
Drying Time ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Spray Inoculation ◽  
Number Of Cells

The effects of method for applying inoculum and of drying time after inoculation on survival and recovery of foodborne pathogens on iceberg lettuce and parsley were studied. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to lettuce and parsley by dip, spot, or spray inoculation methods. Inocula were dried for 2 h at 22°C or for 2 h at 22°C and then 22 h at 4°C before being treated with water (control) or chlorine (200 μg/ml). Significantly higher populations (CFU per lettuce or parsley sample) of E. coli O157:H7 and Salmonella (α = 0.05) were recovered from dip-inoculated produce than from spot- or spray-inoculated produce. This difference was attributed to larger numbers of cells adhering to lettuce and parsley subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from lettuce inoculated by spot and spray methods were not significantly different, but populations recovered from spot-inoculated parsley were significantly higher than those recovered from spray-inoculated parsley, even though the number of cells applied was the same. Significantly different numbers of L. monocytogenes were recovered from inoculated lettuce (dip > spray > spot); populations recovered from dip-inoculated parsley were significantly higher than those recovered from spot- or spray-inoculated parsley, which were not significantly different from each other. Populations of pathogens recovered from lettuce and parsley after drying inoculum for 2 h at 22°C were significantly higher than or equal to populations recovered after drying for 2 h at 22°C and then for 22 h at 4°C. Significant differences (water > chlorine) were observed in populations of all pathogens recovered from treated lettuce and parsley, regardless of inoculation method and drying time. It is recommended that spot inoculation with a drying time of 2 h at 22°C followed by 22 h at 4°C be used to determine the efficacy of chlorine and other sanitizers in killing foodborne pathogens on lettuce and parsley.

Evaluation of Inoculation Method and Inoculum Drying Time for Their Effects on Survival and Efficiency of Recovery of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes Inoculated on the Surface of Tomatoes

2004 ◽  
Vol 67 (4) ◽  
pp. 732-741 ◽  
Author(s):  
MEGAN M. LANG ◽  
LINDA J. HARRIS ◽  
LARRY R. BEUCHAT
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Foodborne Pathogens ◽  
Escherichia Coli O157 ◽  
Water Control ◽  
Drying Time ◽  
E Coli ◽  
Inoculation Method ◽  
Spray Inoculation ◽  
Population Sizes

A study was undertaken to evaluate methods for applying inoculum and to examine the effect of inoculum drying time on survival and recovery of foodborne pathogens inoculated onto the surface of raw, ripe tomatoes. Five-strain mixtures of Escherichia coli O157:H7, Salmonella, or Listeria monocytogenes were applied to tomatoes by dip, spot, or spray inoculation methods. Inocula were dried for 1 or 24 h at 22°C before tomatoes were treated with water (control) or chlorine (200 μg/ml). Significantly (α = 0.05) larger populations (CFU per tomato) of E. coli O157:H7 and Salmonella were recovered from dip-inoculated tomatoes than from spot- or spray-inoculated tomatoes. This difference was attributed to larger numbers of cells adhering to tomatoes subjected to dip inoculation. Populations of E. coli O157:H7 and Salmonella recovered from spot- and spray-inoculated tomatoes containing the same initial number of cells were not significantly different. Significantly different L. monocytogenes population sizes were recovered from inoculated tomatoes (dip > spot > spray). Populations of pathogens recovered from tomatoes were significantly larger when inocula were dried for 1 h compared with 24 h. Significant differences (water > chlorine) were observed in the sizes of populations for all pathogens recovered from tomatoes treated with chlorine, regardless of inoculation method or drying time. Results indicate that inoculation method, drying time, and treatment affect survival and/or recovery of foodborne pathogens inoculated onto the surface of tomatoes. We recommend that spot inoculation with a drying time of 24 h at 22°C be used with standard methods to determine the efficacy of chlorine and other sanitizers for killing foodborne pathogens on tomatoes.

Growth of Escherichia coli O157:H7, Salmonella Typhimurium DT104, and Listeria monocytogenes in Dark Cutting Beef at 10 or 22° C†

2002 ◽  
Vol 65 (1) ◽  
pp. 196-198 ◽  
Author(s):  
C. A. HOOPER-KINDER ◽  
P. M. DAVIDSON ◽  
S. K. DUCKETT
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Salmonella Typhimurium ◽  
Foodborne Pathogens ◽  
Ground Beef ◽  
Growth Characteristics ◽  
Escherichia Coli O157 ◽  
E Coli

An experiment was conducted to determine the effects of the dark, firm, and dry (DFD) condition of beef on growth of the foodborne pathogens Escherichia coli O157:H7, Salmonella Typhimurium DT104, and Listeria monocytogenes Scott A in ground beef. Longissimus muscles from a DFD carcass (pH = 6.45) and normal carcass (N; pH = 5.64) were ground and samples obtained (100 and 0% DFD, respectively). Equal amounts of the 0 and 100% DFD ground samples were mixed to obtain 50% DFD samples. Inoculated 0, 50, and 100% DFD samples were packaged into oxygen-permeable overwrap and stored at 10°C for E. coli O157:H7, Salmonella Typhimurium DT104, and L. monocytogenes Scott A or at 22°C for E. coli O157:H7. Growth characteristics of E. coli O157:H7, Salmonella Typhimurium DT104, and L. monocytogenes Scott A did not differ (P > 0.05) between 0 and 100% DFD. Results indicated that the DFD beef used in this study was no more susceptible to growth of E. coli O157:H7, Salmonella Typhimurium, or L. monocytogenes Scott A than N beef.

Survival of Bacterial Pathogens in Pasteurized Process Cheese Slices Stored at 30°C

1998 ◽  
Vol 61 (3) ◽  
pp. 290-294 ◽  
Author(s):  
KATHLEEN A. GLASS ◽  
KRISTINE M. KAUFMAN ◽  
ERIC A. JOHNSON
Keyword(s):  
Escherichia Coli ◽  
Staphylococcus Aureus ◽  
Listeria Monocytogenes ◽  
Foodborne Pathogens ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Salmonella Serotypes ◽  
Sterile Plastic ◽  
Process Cheese ◽  
Plastic Sample

Six lots of commercial pasteurized process cheese slices were evaluated for the ability to support the growth of four foodborne pathogens, Listeria monocytogenes, Staphylococcus aureus, Salmonella serotypes, and Escherichia coli O157:H7, during 4 days of storage at 30°C. Individual cheese slices were inoculated separately with each pathogen to yield ca. 103 CFU/g. Slices were packaged in sterile plastic sample bags and stored at 30°C for up to 96 h. Populations of Salmonella serotypes and Escherichia coli O157:H7 decreased an average of 1.3 and 2.1 log10 CFU/g, respectively, by 36 h and Salmonella serotypes decreased an additional 0.6 logi0 CFU/g during the remaining 60 h. Populations of Listeria monocytogenes also decreased, although to a lesser extent, exhibiting approximately a 0.6-log10 CFU/g reduction in 96 h. Staphylococcus aureus levels remained relatively constant during the testing period, and were below levels that support detectable enterotoxin production. The process cheese slices tested allowed survival but did not support rapid growth of S. aureus, whereas populations of L. monocytogenes, E. coli O157:H7, and Salmonella serotypes decreased during the 96-h storage at 30°C.

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